1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus for reproducing recorded data at a variable speed through a rotational head helically scanned and a method for controlling an inclination angle of a rotational drum on which the rotational head of the magnetic recording and reproducing apparatus is attached.
2. Description of the Related Art
In a helical scan type magnetic recording and reproducing apparatus represented by a household video tape recorder (VTR), recorded data is generally reproduced at a variable reproducing speed differing from a recording speed in a so-called variable speed reproducing mode. In this case, because the reproducing speed differs from the recording speed in a variable speed reproduction, a locus of a rotational magnetic head attached on a rotational drum on a magnetic tape does not accurately agree with a truck formed on the magnetic tape in a recording operation. Therefore, the track cannot be accurately traced by the magnetic head, and a quality of a reproduced signal is degraded. In particular, as the reproducing speed is heightened, the number of tracks crossed by the magnetic head is increased. As a result, a signal/noise (S/N) ratio is degraded, and noises formed in horizontal stripes occur in a reproduced image.
Also, in a VTR for business use used in a broadcasting station or the like (For example, No. BR-S525 in a VTR for business use manufactured by Vitor Company of Japan, Ltd.), an actuator embodied by a movable coil is attached to a rotational head to displace the rotational head for the purpose of solving the above drawbacks. However, because it is required that the actuator is placed inside a rotated drum, the configuration of the VTR is complicated, and the manufacturing of the VTR is not easy. In addition, the connection of an electric source for the actuator is not easy, a control circuit for controlling the actuator is required. Therefore, the VTR becomes expensive, the VTR is not used for a household apparatus.
2.1. Previously Proposed Art
Also, a method for inclining the whole rotational drum to displace the rotational head attached on the rotational drum is disclosed. However, an apparatus operated according to the method is not manufactured. The reason is that the technique for inclining the rotational drum is not sufficiently advanced and a signal processing technique in a feed-back system is not sufficiently advanced to accurately trace a track on a magnetic tape. In the Victor company of Japan, Ltd. relevant to the present inventor, a technique for accurately controlling an inclination of a rotational drum at a desired angle at a high responsibility has been developed, and two Japanese patent applications have been filed (the name of invention common for the applications: magnetic recording and reproducing apparatus, the filing date: Feb. 22, 1995, and Feb. 28, 1995). The applications have not been laid open, and the technique is not an opened prior art. A rotational drum operated according to the technique is called a dynamic drum. In detail, the dynamic drum is inclined by a rotational power generated by an inclination angle changing motor, and a rotational angle provided by the motor is controlled by a microcomputer. An inclination angle of the dynamic drum is detected by a counter in which a FG pulse signal generated in synchronization with the change of the rotational angle is counted. In addition, a sensor for generating a reset signal is provided to reset the counter when the dynamic drum is inclined at a predetermined inclination angle.
2.2. Problems to be Solved by the Invention
In cases where a variable speed reproduction in a VTR is performed according to the method for inclining the whole rotational drum or in cases where a variable speed reproduction in a VTR is performed by using the dynamic drum, a drum inclination angle corresponding to each of the recording tape speeds and each of the reproducing tape speeds is predetermined, and one of the drum inclination angles is selected. In this case, when a so-called self-recording/reproduction in which the recording and reproduction are performed in the same VTR is performed, one drum inclination angle can be properly selected, and the reproduction can be favorably performed. However, when a so-called interchangeable reproduction in which data recorded in a first VTR are reproduced in a second VTR differing from the first VTR is performed, because mechanical characteristics of a tape running system in the first VTR differ from those in the second VTR, a track pattern formed on a magnetic tape in the recording operation does not perfectly agree with a trace pattern formed on the magnetic tape in the reproducing operation. Therefore, there is a drawback that noises occur in a reproduced image.
Also, there is a case that an actual inclination angle of a rotational drum fluctuates from a predetermined inclination angle because of friction and/or abrasion occurring in a mechanical system for inclining the rotational drum. In cases where the actual inclination angle fluctuates, even though the self-recording/reproduction is performed, there is another drawback that the trace pattern does not agree with the track pattern unless the predetermined inclination angle is changed to compensate the fluctuation of the actual inclination angle.